This proposal is designed to test hypotheses that 1) intraluminal bile salt composition, 2) dietary fatty acid composition, and 3) genetic variations affect cholesterol absorption and cholesterol synthesis. Pilot studies were performed to evaluate feasibility of the experimental approach on 2 subjects which have been completed. Biliary bile acid composition was altered as expected with ursodeoxycholic acid treatment and expected effects on cholesterol absorption and synthesis observed. Acquisition of extramural funding will determine when additional studies will be performed.